In The Journal of the Acoustical Society of America, Vol. 26, No. 1, January 1954, Vonnegut described a sonic device consisting of two coaxial cylindrical cavities. Either compressible or incompressible fluids, for example, air or water, respectively, were tangentially introduced into the larger cylindrical chamber producing an initial vortex. As the fluid entered the smaller chamber, it underwent an increase in angular velocity as the result of the conservation of angular momentum. Fluid in vortical motion in the first cylindrical cavity which passed into the second cavity produced an intense stable acoustical disturbance at the exit of the outlet cavity. Vonnegut discovered that the frequency of the disturbance exhibited roughly linear dependence upon the volume fluid flow rate or upon the square root of the pressure gradient of the fluid entering the first cavity. He empirically determined that the relationship between the frequency of the disturbance, the diameter of the exit orifice, and the pressure gradient could be expressed by the following equation: ##EQU1## where: f=frequency of the disturbance
V.sub.c =speed of sound PA1 D=diameter of the exit orifice PA1 P.sub.1 =entering pressure PA1 P.sub.2 =exhaust pressure PA1 .alpha.=constant less than 1
Vonnegut concluded that his whistle structure amounted to nothing more than an amusing musical toy and, with further development, be concluded that it may be found to have some merit as a musical instrument.
Prior attempts have been made to increase the power output of a sonic whistle by various means. For example, in Sources of High-Intensity Ultrasound, Vol. 1, Plenum Press, New York, 1969, it is taught that with a decrease nozzle diameter and corresponding increase in frequency, the mass flow of a fluid diminishes which, in turn, diminishes the radiated power from a whistle structure. Various multi-whistle designs were then explored with the common problem that multi-whistle gas jets of low internal impedance suffer a disruption of air flow in individual whistles due to air flows of adjacent whistles. There was no disclosure concerning how this problem could be solved and the conclusion was reached that synchronization of whistles was not feasible.
It has been understood for quite some time that sound waves could be used, for example, to coagulate small, suspended particles in a fluid media. For example, in Sonics, John Wiley & Sons, Inc., New York, London, 1955, Hueter and Bolt discussed the effect of simple sonic energy on aerosol processing noting that a sound wave incident on a suspension of small particles in a medium will impart vibratory motion to the particles and that small particles will follow the vibration more readily than larger ones. This was taught to cause relative motion between large and small particles resulting in collisions and agglomeration. The source of ultrasonic waves employed by Hueter and Bolt was a powerful generator causing a thin diaphragm in a tank to vibrate.
It has also been taught that ultrasonic waves can be used to break up larger particles into smaller ones forming a stable dispersion. In Ultrasonics, Marcel Dekker, Inc., New York, 1973, pages 467-471, Ensminger disclosed the production of aerosols by ultrasonic means.
Although the physical mechanisms at work in both the case of coagulation and dispersion or atomization are complex and not fully understood, two formulae can be gleaned from the literature which illustrates the relationship between particle size and optimum ultrasonic frequency for a given process. In general, for coagulation of particles with diameter d, in microns, EQU optimum frequency=(89.6/.rho.d.sup.2).times.10.sup.3 Hz.
where .rho. is in grams/cc.
For a dispersion of particles with diameter d, in microns, EQU optimum frequency=(145/d).times.10.sup.6 Hz.
It is apparent that at modest frequencies micron size particles may be coagulated into larger particles, but considerably higher frequencies are required to produce a dispersion of particles with 10-fold greater diameters. Before the present invention, ultrasonic devices to sonically disperse and coagulate particles in a fluid media have been costly and inefficient and often required electrical energy input. Although the prior art has discussed the abstract principles of sonically coagulating and dispersing suspended particles in a fluid, devices which could accomplish these phenomenon have found little practical application.
U.S. patent application Ser. No. 4,818, filed Jan. 19, 1979, now U.S. Pat. No. 4,253,508, discloses the device of the present invention for coagulation in a fluid media, and it has now been found that the sonic device disclosed as the present invention is capable of performing a wide range of fluid processing operations. Unlike any other sonic devices which have been disclosed heretofore, the device of the present invention presents an extremely low impedance to fluid flow and thus is ideally suited for fluid processing applications where either pure acoustic (sonic or ultrasonic) energy and/or controlled turbulence is desired. No other sonic device prior to the present invention has been capable of multiplying the frequency and power of fluid vortex vibration without significantly altering the impedance of the generator or using significantly higher input power. In addition, the device is found to have an inherent stability both in its fluid flow characteristics as well as in the sonic and ultrasonic wave frequencies it produces.